Apparatus for tensioning of a fabric in a paper machine

Abstract: The invention concerns an apparatus for tensioning of a fabric in a paper machine, such as a press felt (20), a drying wire (10), or of an equivalent fabric. The tensioning apparatus comprises a tensioning roll (30) fitted inside the loop of the fabric, the bearing supports (35a,35b) of said roll (30) being fixed, at the driving side and at the operating side of the machine, to sledges (40a,40b). These sledges (40a, 40b) are arranged to be displaceable by means of a motor (37), synchronously in relation to one another, so as to tighten the fabric (10,20) that runs over the tensioning roll (30) to a certain tension (T). Said sledges (40a,40b) are fitted in connection with the frame part (24;130) of the machine on linear guides (42,44), which can be loaded in different directions transverse to the direction (B) of movement of the sledges (40a,40b). In view of displacing the sledges (40a,40b), shafts (51a,51b) operated by a motor (37) are journalled on the sledges, said shafts (51a,51b) being interconnected by means of a synchronization shaft (36) between the driving side (KP) and the operating side (HP).

Description: The invention concerns an apparatus for tensioning of a fabric in a paper machine, such as a press felt, a drying wire, or of an equivalent fabric, and concerns particularly an apparatus according to the preamble of claim 1, being based on DE-A-30 26 429. In a paper machine, various wires and fabrics are used, such as forming wires, drying wires, and press felts, for all of which the general designation "fabric" will be used in the following. The loops of these fabrics must be tensioned to a certain tension T, which is, as a rule, set in the range of T ≈ 1...5 kN/m. Moreover, inside said fabric loops, an alignment roll is used, by means of whose axial alignment the transverse position of the fabric is controlled. In the prior art, a number of different devices for tensioning of the fabrics in a paper machine are known. The solution that is used most commonly is probably a tensioning device in which the tensioning roll is mounted at the operating side and at the driving side of the machine on carriages, which are displaced synchronously with one another on rollers inside a box beam attached to the frame part of the paper machine. The prior-art fabric-tensioning devices have involved several drawbacks, which will come out in more detail later. Thus, the principal object of the present invention is to provide a novel apparatus for tensioning of fabrics, such as of a press felt or a drying wire or equivalent, by whose means said drawbacks are eliminated. The prior art with its drawbacks will be described in more detail later, reference being made to Figs. A and B in the accompanying drawing. In view of achieving the objectives stated above and those that will come out later, the invention has the features defined in the characterizing portion of claim 1. According to the invention, an apparatus for tensioning of a fabric in a paper machine is provided that is of small size, low friction, and whose position can, thus, be adjusted precisely without hysteresis. The invention also provides the advantage that the suspension of the tensioning apparatus can be made almost free of play and, thus, rigid and less susceptible of vibration. It is a further advantage that, when linear guides in accordance with the invention are used, the sledges of the tensioning apparatus can be supported in all directions transverse to their directions of movement, for which reason the tensioning apparatus can be placed, without changes in the construction, in any position whatsoever, even in a position hanging down on support of its linear guides. It is a further advantage that the tensioning apparatus in accordance with the invention can be assembled and tuned outside the machine and be installed in its site of operation afterwards, which is also of importance because the ball-bearing linear guides, which are used preferably in the invention, require very precise installation. In the following, the prior art most closely related to the invention, problems involved in the prior art, and some preferred embodiments of the invention will be described in more detail with reference to the figures in the accompanying drawing. Figure A shows a prior-art tensioning device for a drying wire in the dryer section of a paper machine. Figure B shows a prior-art upper-felt tensioning device in the dryer section of a paper machine. Figure 1 shows an apparatus in accordance with the present invention for tensioning of a drying wire in a dryer section, in a way corresponding to Fig. A. Figure 2 shows an apparatus in accordance with the present invention for tensioning of an upper felt in a dryer section, in a way corresponding to Fig. B. Figure 3 is a side view of a press section tensioning apparatus as shown in Fig. 1. Figure 4 shows the same as Fig. 3, viewed from above. Figure 5 shows a press section tensioning apparatus as viewed in the direction C-C indicated in Fig. 3. Figure 6 shows vertical sections along the lines D-D in Figs. 3 and 7. Figure 7 shows an apparatus as shown in Fig. 2 for tensioning of a felt loop in a press section, in a way corresponding to Fig. 3. Figure 8 shows a tensioning apparatus as shown in Fig. 7, viewed from above. Figure 9 shows an apparatus as shown in Figs. 7 and 8 as viewed in the direction C-C indicated in Fig. 7. Figure 10 shows a linear ball-bearing guide that is used preferably in tensioning apparatuses in accordance with the invention. Fig. A is a schematic side view of a single-wire group in a multi-cylinder dryer of a paper machine, in which a prior-art drying-wire tensioning device 110 and an alignment device 100 are used. The dryer group shown in Fig. A comprises drying cylinders 11 placed in the upper row and reversing suction cylinders 12 placed in the lower row, the drying wire 10 being passed over said cylinders so that, on the upper cylinders 11, the paper web W to be dried is placed in direct contact against the heated faces of the cylinders 11, and on the reversing suction cylinders 12 at the side of the outside curve. At the right side of Fig. A, the drying wire 10a of the next cylinder group, its guide roll 13a, and the drying cylinder 11a are shown. The drying wire 10 is conditioned by means of the devices 15. On the top of the frame part 130 of the dryer group, there is an auxiliary frame, which comprises vertical parts 28a and 28b as well as a horizontal part 29, the prior-art drying-wire 10 alignment device 100 being fitted on said horizontal part 29 of the auxiliary frame, and the axial alignment of the alignment roll 60 being controlled by means of the bellows 101 and 102 placed inside the U-shaped frame part 103 of said alignment device. The drying wire 10 is guided by the guide rolls 13 and tensioned by the tensioning roll 30 in the device 110. The prior-art tensioning device 110 as shown in Fig. A comprises a tensioning roll 30, which is mounted on a carriage 116. The carriage 116 is displaced on its wheels 117 and 118 on a beam 119 by means of cables 111 and 112, which run over reversing pulleys 113 and 114, of which pulleys the pulley 114 is driven by a motor 115. When the carriage 116 and the connected tensioning roll 30 are displaced by means of the motor 115 in the direction of the arrow B, the tension T of the loop of the drying wire 10 can be regulated. A drawback in the tensioning device 110 as shown in Fig. A is the high friction and the great play at the suspension of the carriage 116 and at the guides, with the resulting vibrations. Further, the construction is quite spacious, as its length in the machine direction is typically 5...6 metres. Further, between the fastening points of the cables 111 and 112 and the rollers 117,118, there is a considerable distance, which produces a detrimental torsion. These drawbacks are avoided by means of the apparatus in accordance with the present invention for tensioning of a drying wire as shown in Fig. 1. In the following, with reference to Fig. B, a prior-art tensioning device 120 for a press felt 20 of the press section in a paper machine and the environment of application of said device will be described. Fig. B shows a compact press section of a paper machine, which press section comprises a suction roll 22a, a smooth-faced centre roll 21, and a press roll 22b. In connection with the centre roll 21, the second and the third nip N 2 and N 3 of the press section are formed. The first press nip (not shown) is formed underneath the suction roll 22a. Through the nip N 3 , the press felt 20 runs, which is guided by the guide rolls 23 and by the alignment roll 60 and tensioned by the tensioning roll 30. In connection with the frame part 24 of the paper machine, at the operating side of the machine, there are openable intermediate pieces 25, after whose opening the upper felt 20 can be replaced. The prior-art alignment device 100 for the control of the transverse position of the upper felt is substantially similar to that described above in relation to Fig. A. Fig. B shows a prior-art felt 20 tensioning device 120, which comprises carriages 121 placed at the driving side and at the operating side of the machine, the tensioning roll 30 of the felt loop being mounted in connection with said carriages 121. The carriage 121 has been arranged to move on the guides 123 mounted on the frame parts, being operated by a drive shaft 122. The device 120 includes a stationary rack 124, in connection with which there is the cogged wheel 125 on the drive shaft 122 so as to displace the carriage 121 and to tension the felt 20. At both ends of the shaft 122, hydraulic motors are fitted, from whose pressures the tensioning force of the device 120 can be measured. The construction of the tensioning device 120 involves some of the same drawbacks as the drying-wire 10 tensioning device 110 described above, and, moreover, the tensioning device is spacious in the vertical direction (H ≈ 1200 mm). Further, the rigidity of the device is quite little, which causes drawbacks, such as a tendency of vibration. These drawbacks are eliminated by means of the novel apparatus shown in Fig. 2. In the following, with reference to Fig. 1, the principal features of the construction of the apparatus in accordance with the present invention for tensioning of the drying wire 10 will be described. The environment of application was described above in relation to Fig. A. Fig. 1 also schematically shows the apparatus for displacement of the alignment roll 60, which apparatus comprises a sledge 64, on which one of the bearing supports 63 of the alignment roll 60 is mounted. The sledge 64 is displaced in the direction of the arrow A on a guide 26 fitted on the frame part 29 by means of the power of a motor 61. As is shown in Fig. 1, the axle journals 31a and 31b (Fig. 4) of the tensioning roll 30 for the drying wire 10 are mounted on sledges 40 by means of bearing supports 35, which sledges are arranged to be displaceable along the linear guides 42,44 in the direction of the arrow B by means of a shaft 36 driven by a motor 37 so as to tension the wire 10. In the following, with reference to Figs. 3 to 6, a preferred exemplifying embodiment of the construction of a wire 10 tensioning apparatus placed in a position as shown in Fig. 1 will be described. By means of the tensioning apparatus, the tensioning roll 30 can be displaced in the direction of the arrow B so that the wire 10 can be brought to the desired tension, which is, as a rule, in the range of T ≈ 1...5 kN/m. The tensioning roll 30 is journalled by means of its axle journals 31a,31b in bearing supports 35a,35b, which are attached to the sledges 40a,40b of the tensioning device. In the reference denotations, a refers to devices at the operating side (HP), and b to devices at the driving side (KP). With the exception of the drive motor 37, the construction can be made symmetric in relation to the vertical centre plane in the machine direction. To the sledge 40a at the operating side, the drive motor 37 is fixed, whose shaft 51a is mounted by means of bearings 52 on the sledge 40a. The shaft 51a is connected to the shaft 51b at the driving side by means of an intermediate shaft 36, said shaft 51b being mounted on the sledge 40b at the driving side by means of bearings 52 (Fig. 6). On the frame part 130 of the dryer section, base plates 48a,48b are fixed, on which the pairs of guides 42 are fixed, whose guides 42 are placed at a small horizontal distance P ≈ 100...300 mm from one another. On the pairs of guides 42, linear bearings 44 move, whose construction will be described in more detail later with reference to Fig. 10. The bearings 44 are attached to sledges 40a and 40b. On support of the base plates 48a,48b and in the spaces between the pairs of guides 42, racks 41a,41b are attached, with which the cogwheels 50a,50b on the shafts 51a,51b driven by the motor 37 are in tooth engagement. In this way the transmission is formed from the motor 37 for displacement of the sledges 40a,40b, synchronized by means of the shaft 36, so as to tension the loop of the drying wire 10 in the direction of the arrow B indicated in Fig. 1. In Fig. 3, the tensioning roll 30 with its sledges 40a,40b is shown in its left extreme position, and so is the shaft 51, whose right extreme position is, in Fig. 3, denoted with the reference 51'. Thus, the tensioning roll 30 and its sledges 40a,40b can move through the distance L 1 . In the construction shown in Fig. 3, the relative distance H 0 between the plane of support of the linear guides 42,44 and the racks 41a,41b can be made relatively short, preferably H 0 ≈ 100...200 mm. Thus, the raising force produced by the transmission between the motor 37, the drive shafts 51, the cogwheels 50a,50b, and the racks 41a,41b is reduced, which force is received by four linear ball-bearing units 44, which are carrying in four opposite directions. In the following, with reference to Figs. 2,7,8 and 9, a preferred exemplifying embodiment of the construction and operation of a press-felt 20 tensioning apparatus in accordance with the present invention, placed in a position as shown in Fig. 2, will be described. In Fig. 2, the tensioning apparatus is placed on the frame part 24 of the press, and the construction and the operation are substantially similar to those described in relation to Figs. 3 to 6, and in all the Figures 1 to 10, the same reference denotations are used for corresponding parts. The constructions are to such an extent similar that Fig. 6, which was described above, is, at the same time, a sectional view taken along the line D-D drawn both in Fig. 3 and in Fig. 7. Thus, in the following, only those features will be described in whose respect the tensioning apparatuses for the press-felt 20 tensioning roll illustrated in Figs. 7,8 and 9 differ from the corresponding apparatuses for the drying wire 10, illustrated above in Figs. 3 to 6. In the apparatus shown in Figs. 7 to 9, above the guides 42 and above the racks 41a,41b placed between said guides, a telescopic deck construction 52 is used, by whose means access of contaminations, such as splashes, to the guide parts is prevented. Moreover, in Fig. 7, a so-called splice-turning device 53 is seen, by whose means the alignment of the tensioning roll 30 can be altered slightly by shifting the bearing support 32a in relation to the sledge 40a. The splice-turning device comprises a worm gear rotated by a drive shaft 55, by means of which worm gear the bearing support 32a is displaced in the glide guides 54 of the sledge 40a so as to alter the alignment of the roll 30 (Fig. 7). In the following, with reference to Fig. 10, a preferred embodiment of the linear bearing arrangement of the sledges 40a,40b and an exemplifying embodiment of the guides will be described. The pairs of guide rails 42 at the driving side and at the operating side are fixed to the frame beams 24;130 or equivalent by means of screws 43. On the guide rails 42, linear ball bearings 44 move, which are fixed to the sledges 40a,40b by means of screws 45. As comes out best from Figs. 3 and 7, there are three pairs of linear ball bearings 44 as uniformly spaced on both sledges 40a,40b. The linear ball bearings 44 are characterized by high loading capacity in all different directions transverse to the longitudinal direction of the guide rails 42, as well as by rigidity and by adjustable small plays and by relatively low friction. The linear guides of the sledges 40a,40b comprise said guide rails 42, onto which four axial rolling grooves 48 for the bearing balls 46 have been made. On the guide rails 42, the ball-bearing units 44 move, in whose interior there are bearing balls 46, which perform a closed circulating movement in the loops 47a,47b,47c,47d, which numerous successive balls that are "in turn" are supported with their carrying portions in said rolling grooves 48 that are provided on the guide rails 42 in pairs. The rolling grooves 48 on the guide rail 42 are placed in pairs and symmetrically so that each carrying row of bearing balls 46 transfers the contact load between the guide rail 42 and the ball-bearing unit 44 at an angle of about 45° when examined in the sectional plane of Fig. 10. In this way, an equally high loading capacity is obtained in the four different directions, which permits the tensioning apparatuses in accordance with the invention to be placed in all sorts of different positions without substantial alterations of construction. The linear guides 42,44 mentioned above are commercially available bearing components in themselves known.

Claims: Apparatus for tensioning of a fabric in a paper machine, such as a press felt (20), a drying wire (10), or of an equivalent fabric, comprising a tensioning roll (30) fitted inside the loop of said fabric, the bearing supports (35a,35b) of said roll (30) being fixed, at the driving side and at the operating side of the machine, to sledges (40a, 40b), which are arranged to be displaceable by means of a motor (37) synchronously in relation to one another on linear guides (42,44) attached to the frame (24,130) of the machine, so as to tighten the fabric (10,20) that runs over the tensioning roll (30) to a certain tension (T), for which displacement shafts (51a,51b) operated by a motor (37) are journalled on the sledges, said shafts (51a,51b) being interconnected by means of a synchronization shaft (36) between the driving side (KP) and the operating side (HP) characterized in that said linear guides (42,44) are arranged loadable in different directions transverse to the direction (B) of movement of the sledges (40a,40b). Tensioning apparatus as claimed in claim 1, characterized in that the drive motor (37) of the sledges (40a,40b) in the tensioning apparatus is attached to one of said sledges, preferably to the sledge (40a) at the operating side (HP) (Fig. 4). Tensioning apparatus as claimed in claim 1 or 2, characterized in that both at the driving side and at the operating side (KP.HP), there are two parallel guide rails (42) at a short horizontal distance (P) from one another, in connection with each of which guide rails. as attached to the sledges (40a,40b), there are at least two linear ball-bearing units (44) placed one after the other. Tensioning apparatus as claimed in claim 3, characterized in that, in the gaps between said pairs of guide rails (42), racks (41a,41b) are provided, which are fixed to the frame parts (24;130) of the machine and at which the teeth on their outer face are in tooth engagement with the cogwheels (50a,50b) on the drive shafts (51a,51b) at the driving side and at the operating side (KP,HP). Tensioning apparatus as claimed in any of the claims 1 to 4, characterized in that said guide rails (42) comprise four axial rolling grooves (48) for the bearing balls, on which grooves the numerous successive bearing balls (46) which perform a loop-shaped circulating movement in the ball bearing units (44) are, each in their turn, supported in respect of their carrying portions (Fig. 10). Tensioning apparatus as claimed in any of the claims 1 to 5, characterized in that said apparatus is substantially symmetric in relation to the vertical centre plane in the machine direction, at least with respect to the arrangement of linear guides (42,44) of said sledges (40a,40b). Tensioning apparatus as claimed in any of the claims 1 to 6, characterized in that the teeth on said racks (41a,41b) are placed relatively close (H 0 ) to the support plane of said guide rails (42), so that their perpendicular distance H 0 ≈ 100...200 mm. Tensioning apparatus as claimed in any of the claims 1 to 7, characterized in that the height H 1 of the tensioning apparatus, calculated from the support plane of the guide rails (42) to the central axis of the tensioning roll (30), is little, preferably of an order of H 1 ≈ 600 mm. Tensioning apparatus as claimed in any of the claims 1 to 8 for a press felt (20) or equivalent, characterized in that the tensioning device comprises a so-called splice-turning device (53), which comprises a power unit (53,55) between one of the bearing supports (35a) of the press-felt (20) tensioning roll (30) and the sledge (40a) placed in connection with said bearing support, as well as a linear guide fitting (54) (Fig. 7). Tensioning apparatus as claimed in any of the claims 1 to 9, characterized in that said guide rails (42) and said racks (41a,41b) between them are covered by telescopic or equivalent shield box constructions (52).

Inventors: AUTIO JUKKA, KUJALA TIMO, AUTIO, JUKKA, KUJALA, TIMO
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21F7
IPC codes: D21F7